In recent years, in the medical field and the industrial field, robot apparatuses have been widely used in order to perform tasks faster with a high degree of accuracy. Commonly, a robot apparatus is a multi-link structure in which a plurality of links are connected with one another by joint units, and as rotary driving in the plurality of joint units is controlled, driving of the whole robot apparatus is controlled.
Here, position control and force control are known as control methods of the robot apparatus and each of the joint units. In position control, for example, a command value such as an angle is provided to an actuator of a joint unit, and driving of the joint unit is controlled according to the command value. Meanwhile, in force control, a target value of force applied to a task target by a whole robot apparatus is given, and driving of a joint unit (for example, torque generated by the joint unit) is controlled such that the force indicated by the target value is implemented.
Generally, most robot apparatuses are driven by position control since it is convenient to control and a system configuration is simple. However, position control is commonly called “hard control” since cannot easily deal with external force flexibly, and position control is not suitable for a robot apparatus performing a task (purpose of motion) while performing physical interaction (for example, physical interaction with a person) with various external worlds. Meanwhile, force control has a complicated system configuration, but can implement “soft control” of a power order, and thus force control is a control method suitable, particularly, for a robot apparatus performing physical interaction with a person and a control method having excellent usability.
For example, as a robot apparatus to which force control is applied, Patent Literature 1 discloses a robot apparatus that includes a movement mechanism configured with 2 wheels and an arm unit configured with a plurality of joint units, and performs control such that the wheels and the joint units are driven in a cooperative manner as a whole (performs whole body cooperative control).
Further, in force control, it is necessary to detect torque (including generated torque generated by a joint unit and external torque given from the outside to the joint unit) with a high degree of accuracy in each joint unit of a robot apparatus, and perform feedback control and/or feedforward control. For example, Patent Literature 2 discloses a torque sensor that includes a decoupling structure, and performs high-accuracy torque detection in which influence of vibration is reduced as much as possible.